If US Prisons suddenly became a US state...

They would be the 39th large US state...

With 12 of the 50 US states having smaller populations.

As these States (and D.C. would have smaller populations).
39 West Virginia
40 Hawaii
41 New Hampshire
42 Maine
43 Montana
44 Rhode Island
45 Delaware
46 South Dakota
47 North Dakota
48 Alaska
– District of Columbia
49 Vermont
50 Wyoming